Receiving apparatus for communication systems



July 18, 1939. L.. D. wHl'rELocK ECEIVING APPARATUS FOR COMMUNICATION SYSTEMS Filed July 13, 1937 Patented `luly 18, 1939 UNiTED smits PATENT OFFiCE RECIVING APPARATUS FOR CMMUNICATION SYSTEMS Leland I). Vlhitelock, Wilkinsburg, Fa., assigner to The Union Switch & Signal Company,

12 Claims.

lilly invention relates to receiving apparatus for communication systems, and particularly to receiving apparatus for communication systems using `carrier suppressed single side band trans- 5 mission, I

I shall describe one form vof apparatus ernbodying `my invention, and shall then point out the novel features thereof in claims.

A feature cf my invention is the provision of i" communication system receiving apparatus which uses the superheterodyne principle and includes novel and improved means of frequency combination for demodulation. Another feature of my invention is the provision of receivh ing apparatus of the type here involved having .a high degree of sensitivity and selectivity. Still anotherv feature of my invention is the provision of receiving apparatus using the superheterodyne principle which is susceptible of superrel generation. Other features and advantages of my invention will ,appear as the specification progresses.

Modulation means that the amplitude of a carrier voltage varies as the amplitude of a mody-f ulation voltage. Such variation can be obtained by impressing simultaneously voltages of the carrier andthe modulation frequencies upon a device Whose response is not proportional to the voltage applied. When using multi-electrode :ci electron tubeswith carrier voltage on one grid and modulation voltage on another grid, direct multiplication of the carrier and modulation voltages results. In general, according to my invention, a carrier suppressed single side band :ii communication current, such as .an upper side band carrier telephone current, is mixed with a high carrier frequency in a first detector or mixer tube. The output of the first detector tube is fed through selecting circuits, prefer- .;1-1 ably including an intermediate frequency amplinena-nd in which circuits one of the side bands resulting from modulation of the high frequency carrier with the incoming communication current energy is selected `and amplified and the remaining side band is rejected. A small portion cf the high frequency carrier may be passed by the selecting circuits and amplified along with the selected side band. Such selection is accomplished easily as the ltwo side bands appearing .is in the output of the first detector are separated from each other by twice the value of the frequency of the original carrier of the received fcommunicationcurrent. In a second detector or `dernodulator tube, the frequencies passed by the te selecting circuits are mixed withv the energy (Cl. Z50-20) suppiied from a local oscillator which generates a carrier having a frequency corresponding to the original carrier of the received current. The resulting products of dernodulation are passed through a band pass filter which is proportioned i) to pass the band of the original modulation frequencies and to suppress frequencies both .above and below such band. Superregeneration can be effected at the second detector.

For a better understanding of my invention, reference may be had to the accompanying drawing, which is a diagrammatic view of one form of apparatus embodying my invention.

To assist in the understanding of the apparatus, I shall assume by Way of illustration that the communication current to be received is an upper side band carrier telephone current, the carrier being of 7000 cycles per second and the voice frequency range extending from 500 to 2500 cycles per second. Under such conditions, the communication current has a frequency range of 7500 to 9500 cycles. Furthermore, I shall .assume that the local high frequency carrier is of say, 500,000 cycles per second. The local low frequency carrier is of '7000 cycles, the '3 same as the original carrier of the telephone current. It is to be understood, of course, that my invention is not limited to these frequencies, and other frequencies may be used, if desired.

Referring to the drawing, the apparatus the ""0 forrn here illustrated, consists of eight distinctive units or devices, together with `a receiving circuit and an output circuit. The apparatus also includes, of course, proper sources of current and circuit connections. These eight units or devices are, for the sake of clearness, shown each enclosed by dash and dot lines and can be identified as `a first detector FD, an intermediate frequencyamplifier IFA, a second detector SD, an amplifier AM, a band pass filter BPF, an '1U audio frequency amplifier AFA, a high frequency oscillator HFO and a low frequency oscillator LFO. These several units will be taken up in' turn and described, after which the operation of the apparatus as a whole will be pointed out.

The circuits for heating the filaments of the electron tubes of the several different units are not shown for the sake of simplicity, and it Will be understood that the filament of each electron u tube is heated so that the tube is in an active con- "9 dition, the several filaments being connected with a proper source of current either in parallel or in series, as desired.

The first detector FD comprises an electron tube 2, an input transformer TI and an output 55 transformer T2. The electron tube 2 may be of any one of several different types, and in this instance is a heptode provided With a cathode 3, an anode 4 and five grids, grids 5 and 6 being used as control grids, and the other three grids being used as suppressor and screen grids. The cathode 3 is connected over a grid biasing unit 1 With a common ground Wirev 8, which in turnis connected with a ground electrode 9 to form a ground connection common to the several units. The control grid 5 of tube 2 is connected with one terminal of the secondary winding I of the input transformer TI, the other terminal of which winding is connected over wire with the common ground Wire 8 to complete a circuit for the control grid 6. A condenser 16 is preferably connected across the secondary winding I0 of transformer TI. The primary winding I2 of transformer TI is interposed in a receiving circuit which also includes a receiving coil RC and a condenser I3. The receiving coil RC would be coupled in any convenient manner with the transmitting circuit, not shown, over which the communication current is sent out from a remote transmitter, In case the communication current is the assumed upper side band carrier telephone current, the coil RC would be coupled with the metallic telephone circuit. In case the transmission is effected by means of radiated electromagnetic waves, the receiving coil RC would be coupled to or made an integral part of the antenna system. Again, the coil RC may be of the customary loop antennatype. The condenser I3 and the coil RC are proportioned to tune the receiving circuit for efficient reception of the specific communication current. The control grid 5 of tube 2 is connectedover wire I4 with one output terminal of the high frequency oscillator HFO, to be described later on, the other output terminal of oscillator HFO being connected with the ground to complete a grid circuit for the grid 5.

The plate circuit of tube 2 can be traced from the positive terminal of a generator G over Wire I5, resistor I6, wire I1, primary winding I8 of the output transformer T2, plate 4, intervening tube space to cathode 3, biasing unit 1, wire 8, ground electrodes 9 and I9, and wire 20 to the negative terminal of generator G. f

On the assumption that the communication current is an upper side band carrier telephone current of a frequency range of '7500 to 9500 cycles, and that the high frequency carrier impressed on the grid 5 of tube 2 is of'500,000 cycles, the resulting modulation gives in the plate circuit of tube 2 the carrier frequency of 500,000 cycles, a lower side band of 492,500 to 490,500-cyclesand an upper side band of 507,500 to 509,500 cycles. These three products resulting from modulation are available for inducing electromotive forces of corresponding frequencies in the secondary winding 2| of the output transformer T2.

The intermediate frequency amplifier IFA comprises an electron tube 24 and an output transformer T3. The control grid 25 of tube 24 is provided with a circuit including the secondary winding 2| of the output transformer T2 of the first detector FD, the grid 25 being connected with one terminal of winding 2| and the circuit being completed through a biasing element 26 interposed between the ground Wire 8 and the cathode 21 of tube 24 and the lower terminal of secondary winding 2| being connected with wire 8. The plate circuit for tube 24 extends from the generator G over wire I5, resistor I6, Wires I1 and. 28, primary winding 29 of transformer T3, plate 30 of tube 24, intervening tube space to cathode 2'1`, biasing unit 26, wire 8, ground electrodes 9 and I9, and Wire 20 back to the generator G.

Condensers 22 and 23 are connected across the primary Winding I8 and the secondary winding 2|, respectively, of transformer T2, and are proportioned and adjusted to tune the associated circuits for selecting the upper side band frequencies of 507,500 cycles to 509,500 cycles appearing in the plate circuit of the first detector tube and to substantially suppress the lower side band. These circuits may be proportioned so that a small amount of the carrier frequency of. 500,000 cycles is passed from the first detector tube to the intermediate frequency amplifier, for use in the second detector as will later appear. In this instance, I shall assume that a small amount of the high frequency carrier is passed.. It is not essential that a part of the high fre-l quency carrier be passed through the intermediate:

frequency amplifier IFA, since the high frequency carrier may be fed directly from the highV frequency oscillator HFO to the second detector SD.

in, a manner to appear hereinafter. Condensers and 4| are connected across the windings 29 frequencies in the secondaryr Winding 3| of that transformer.

The second detector SD comprises an. electronV tube 32 and associated input and output circuits. The tube 32y is preferably a heptode similar to the tube 2 of the first detector, the grids 33 and 34 of tube 32 being used as control grids. The control grid 33 is connectedA with onel terminal of the secondary winding 3| of transformer T3 over a grid leak unit 35, and; the other terminal ofv secondary Winding 3| is connected with the cathode 36 of4 tube 32 over wires 64, 8 and.

65. Consequently, the upper side band of 507,500 to 509,500 cycles and the carrier frequency of. 500,000 cycles passed and' amplifiedA through the intermediate frequency amplifier IFA are im pressed upon the control gridV 313 of tube 32. The control grid 34 of tube 33 is connected with the low frequency oscillator LFO, to be described later, over Wire 31, a resistor 38 and a condenser 39 being interposed in the connection. Wire 31 is connectedV with one output terminal of the low frequency oscillator LFO and a second output terminal of oscillator LFO is connectedwith the ground and in turn with the groundwire 8A to complete the circuit for the control grid 34. Thus, the carrier frequency of 7000'cycles from oscillator LFO is impressed upon the control grid 34of tube 32.

The plate circuitv of tube 32 extends from gen-- erator G over Wire 42, resistors 43 and 44 in series, plate 45 `of tube 32, intervening tube space to cathode 3.6, wires and 8, ground electrodes.

9 and I9, and Wire 20 to the generator G.

Since the frequencies impressed upon the control grid 33 of tube 32 consist of the upper side band resulting from modulation of the high frequency carrier by the received telephone current together with the high frequency carrier, andi since the frequency impressed upon the control grid 34 is the carrier. ofthe low frequency oscil- 75.

CFI

li f3 lator, there is produced in the plate circuit of tube 32 a series of thirteen different main products of demodulation. It is believed unnecessary to itemize these various products of demodulam tion and that Yit is suiiicient to point out that oneof the products is theV selected upper side band minus the sum of the two carrier frequencies, and which product is the voice frequency band, that is, the' upper side band of 507,500 to 509,500 cycles minus the sum of high frequency carrier of 500,000 cycles and low frequency carrier of 7000 cycles leaving voice frequencies of 500 to 2500 cycles. In other words. one of the products of demodulation is the origin nal voice modulationfrequencies of the telephone current. The product of deinodulation nearest in frequency to the voice frequency band is the low frequency carrier ol' 700i? eycies. There is sufficient frequency separation, therefore. to allow isolation of the Voice frequency band by means of a band pass, filter designed to pass the voice frequencies. It should alsobe noted that the impedance of the plate circuit of tube 32 will be so low to all demodulation products containing the high frequency carrier of 500,000 cycles that little or no voltage of these frequencies Will appear in the output of the second detector SD.

The second detector SD can be made superrcgenerative by making the detector oscillate weakly at the frequency of 500,000 cycles and by using the lo-w frequency of 7000 cycles as quench frequency, as well as for detection. To accomplish superregeneration, the grids t0, 4l, and 48 of tube 32 are tied together and connected over wire B6 to an intermediate terminal of a resistor 49 connected between wire ft2 of the plate circuit and wire 55 leading to the cathode 36; two condensers 50 and 5l are interposed between the mid terminal of the resistors 43 and 44 of the plate circuit and the wire 00 connecting the grids 46, 47, 48; and the ground wire G is connected to the mid terminal of the condensers 50 and 5| over a wire 1|.

These feed-back connections between the plate circuit of tube 32 and the grids of the tube are so proportioned and adjusted that oscillations of 500,000 cycles are generated. The high froquency carrier impressed upon the grid 32. through the intermediate frequency amplifier holds the detector oscillations in step so that there is no audible beat note from this source. As stated above, the low frequency carrier of '7000 pycles impressed upon the grid 34 of tube 32 acts as a quench frequency.

If desired, the high frequency carrier can be rejected in the output of the rst detector FD along with the lower side band. In this case, the high frequency oscillator HFO would be com nected with the second detector over a connection indicated by the dotted line 52 connected between the wire i4 leading from the high frequency oscillator I-IFO, and the wire 05 con" nected to the grids 4B, 4l, and 48 of tube 32.

The amplifier AM is a single-stage amplifier interposed between the second detector SD and the band pass filter BPF. The amplifier AM includes a triode electron tube 53, the control grid 54 of which is coupled with the plate circuit of the second detector SD. As here shown, the grid 54 is connected through a condenser 55 with an intermediate terminal of the resistor 44 interposed in the plate circuit of the second cletector SD. The circuit for grid 54 is completed through a biasing unit 08 interposed between the cathode 69 and the common ground wire 8. Plate voltage is obtained for plate 31 of tube 53 from the generator G over wires 42 and 'l5 and the primary winding 56 of a transformer T4 which is part of the band pass filter BPF, as will be readily understood by an inspection of the drawing. Hence, the output of the second detector SD is amplified by amplifier AM and passed to the input side of the band pass filter BPF.

The band pass filter BPF comprises windings 00 and 'i of transformer T4, winding i0 of an oitput transformer T5, condensers 5i and 58, and an inductance 59. These windings and condcnscrs are arranged in the usual manner for hand nass filters and are adjusted so as to pass the voice frequency band extending from 500 to 2500 cycles and to substantially suppress frequencies outside of such band. As pointed out hereinbefore, in the products of demodulation i produced at the second detector, the nearest frequency to the voice band is that of the low frequency carrier of 7000 cycles. Consequently, a high degree of selectivity at the band pass filter BPF is obtained.

The audio frequency amplifier AFA consists of an electron tube 5| and an output transformer T0. The voice frequencies appearing inthe windn ing 'l0 of transformer T5 of the filter BPF are impressed between the control grid G0 of tube 6| .'1

of amplifier AFA and the cathode 12, a biasing unit i9 being interposed in the connection. Plate voli-.age is obtained for the plate 13 of tube 6| from the generator G, the circuit being readily understood by an inspection of the drawing and need not be further described except to point out that it includes the primary winding 62 of the output transformer T6. The final output circuit includes the secondary winding 63 of transformer T0 and the operating winding 14' of a loud speaker LS. It is clear that the voice frequencies passed by the filter BPF are further amplified at the amplifier AFA and reproduced at the loud speaker LS.

The high frequency oscillator HFO is of the electron tube type comprising an electron tube 80, having coupled -plate and grid circuits. The parts are so proportioned that the alternating current component of the plate circuit persists and has a frequency, in the case here assumed for illustration, of 500,000 cycles per second. The specific structure of the oscillator HFO may take any of the well-known forms, and it is thought that it will be readily understood by an inspec tion of the drawing and a detailed description thereof is unnecessary except to point out that one output terminal is connected by wire Si with wire i0 leading to the first detector FDl and the other output terminal is connected with the ground electrode I0 and in turn with the ground wire 8. Also, the output of the high frequency oscillator HFO may be connected with the second detector SD through the medium of wires 3i and 52, if desired.

The low frequency oscillator LFO is also of the A electron tube type and includes a pentode '18. The speciiic structure of this oscillator LFO may be that of any of the well-known types and will be readily understood by an inspection of the drawing. It is to be pointed out that the parts are so proportioned that the oscillator LFO generates a carrier frequency of 7000 cycles, which frequency is impressed upon the control grid 34 of the second detector SD.

In describing the operation of the apparatus,

' is that of the 10W frequency carrier.

it is to be understood that normally the electron tubes are all heated and are in an active condition. A carrier telephone current of 7500 to 9500 cycles, when picked up by the coil RC of the receiving circuit, is in turn impressed upon control grid 6 of the first detector tube 2 for modulation of the high frequency carrier of 500,000 cycles impressed upon the control grid 5 of tube 2. The resultant upper side band of 507,500 to 509,500 cycles is selected by virtue of the tuning of the circuits coupling the first detector FD with the intermediate frequency amplifier IFA, A small portion of the high frequency carrier is also passed by the coupling between the first detector and the intermediate frequency amplifier. Such selection is accomplished easily as the two side bands resulting from modulation in the first detector are separated from each other by twice the value of the original carrier frequency of the telephone current. After amplification of the selected frequencies at the intermediate frequency amplifier IFA, such frequencies are impressed upon the control grid 33 of the second detector tube 32. The local carrier frequency of 7000 cycles is impressed upon the control grid 34 of the tube 32. As a result of the mixing of these three frequencies, namely, selected upper side band, high frequency carrier and low frequency carrier, a series of products of demodulation are produced in the plate circuit of the second detector tube 32. One of these products of demodulation is the original modulating voice frequency of the telephone current, Superregeneration is accomplished at the second detector, as Well as demodulation by feed-back connections between the plate circuit and certain of the grids of the tube 32. These several products of demodulation of the second detector SD are amplified by the single-stage amplifier AM and are impressed upon the input side of the band pass filter BPF proportioned to pass the voice frequency band. Of the products of demodulation of the second detector, the one having frequency nearest to the voice frequency band This being so, almost complete isolation of the voice frequencies is effected in the output of the filter. The voice frequencies appearing in the output of the lter are further amplified at the audio frequency amplifier AFA and are reproduced at the loud speaker LS. It is to be noted that the amplifiers AM and AFA may not be required, and also additional stages of amplification may be inserted, if desired. Furthermore, superregeneration can be omitted at the second detector. Again, the high frequency carrier may be suppressed in the output of the first detector FD and energy from the high frequency oscillator HFO supplied directly to the second detector SD, if desired.

Although I have herein shown and described only one form of receiving apparatus for communication systems embodying my invention, it is understood that various changes and modiiications may be made therein Within the scope of the appended claims Without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Receiving apparatus comprising, a first electron tube detector, a second electron tube detector, a source of high frequency carrier current, a source of low frequency carrier current, a receiving circuit proportioned for response to a carrier suppressed single side band communication current having a given signaling frequency band and the carrier of which is of the same frequency as said 10W frequency carrier, means to couple the receiving circuit and said source o f high frequency carrier with the input electrodes of said first detector tube to modulate said high frequency carrier by the communication current picked up by the receiving circuit, coupling means to couple the output electrodes of said first detector tube with the input electrodes of said second detector tube, said coupling means proportioned to select a particular side band resulting from said modulation, other coupling means to couple said source of low frequency carrier and said source of high frequency carrier with the input electrodes of said second detector tube to produce as a product of demodulation the signaling frequency band of said communication current, a signaling device responsive to such signaling frequency band, and means to couple said def vice with the output electrodes of said second detector tube including a band pass filter proportioned to pass such signaling frequency band.

2. Receiving apparatus comprising, a rst electron tube detector, a second electron tube detector, a source of high frequency carrier current, a source of 10W frequency carrier current, a receiving circuit proportioned for response to a carrier suppressed single side band communication current having a given signaling frequency band and the carrier of Which is of the same frequency as said low frequency carrier, means to couple the receiving circuit and said source of high frequency carrier with the Input electrodes of said rst detector tube to modulate said high frequency carrier by the communication current picked up by the receiving circuit, coupling means to couple the output electrodes of said first detector tube with the input electrodes of said second detector tube, said coupling means proportioned to select a particular side band resulting from said modulation and to pass a portion of the high frequency carrier, other coupling means to couple said source of low frequency carrier with the input electrodes of said second detector tube to produce as a product of demodulation, the signaling frequency band of said communication current, a signaling device responsive to such signaling frequency band, and means to couple said device with the output electrodes of said second detector tube including a band pass filter proportioned to pass such signaling frequency band.

3. Receiving apparatus comprising, a first electron tube detector, a second electron tube detector, a source of high frequency carrier current, a source of 10W frequency carrier current, a receiving circuit proportioned for response to a carrier suppressed single side band communication current having a given signaling frequency band and the carrier of which is of the same frequency as said low frequency carrier, means to couple the receiving circuit and said source of high frequency carrier with the input electrodes of said first detector tube to modulate said high frequency carrier by the communication current picked up by the receiving circuit, coupling means to couple the output electrodes of said first detector tube with the input electrodes of said second detector tube, said coupling means proportioned to select a particular side band resulting from said modulation, other coupling means to couple said source of low frequency carrier and said source of high frequency carrier with the input electrodes of said second detector tube to produce as a product of demodulation the signaling frequency band of said communication current, circuit means to couple the anode electrode of the second detector tube with a grid electrode of the tube including resistance and capacitance as required to effect superregeneration for said second detector, a signaling device responsive to such signaling frequency band, and means to couple said device with the output electrodes of said second detector tube including a band pass filter proportioned to pass such signaling frequency band.

4. Receiving apparatus comprising a first electron tube detector, an intermediate frequency electron tube amplifier, a second electron tube detector, a source of high frequency carrier current, a source of low frequency carrier current, a receiving circuit proportioned for responseto a carrier suppressed single side band communication current having a given signaling frequency band and the carrier of which is of the same frequency as said low frequency carrier, means to couple the receiving circuit and said source of high frequency current with the input electrodes of said first detector tube to modulate said high frequency carrier by the communication current picked up by the receiving circuit, coupling means to couple the output electrodes of said first detector tube With the input electrodes of said amplifier tube, said coupling means proportioned to select aparticular side band resulting in said modulation and to pass a portion of the high frequency carrier, other coupling means to couple the output electrodes of said amplifier tube and said source of 10W frequency carrier with the input electrodes of said second detector tube to produce as a product of demodulation the signaling frequency band of said communication current, a signaling device responsive to such signaling frequency band, and means to couple said device with the output electrodes of said second detector tube including a band pass filter proportioned to pass such signaling frequency band.

5. Receiving apparatus comprising, a first eleotron tube detector provided with two control grids, a second electron tube detector provided With two control grids, a receiving circuit proportioned for response to a given carrier suppressed single side band communication current having a given signaling frequency band, a first source of carrier current of a frequency different from the frequency of the carrier of the communication current, a second source of carrier current of the same frequency as the carrier of the communication current, means to connect the receiving circuit with one control grid and said firstsource with the other control grid of the first detector tube to produce side bands of the first carrier and the communication current picked up by the receiving circuit, coupling means to couple the plate circuit of the first detector tube with one control grid of the second detector tube, said coupling means proportioned to select a particular one of said side bands only and to pass a portion of the first carrier, means to connect said second source with the other control grid of the second detector tube to produce as a product of demo'dulation the signaling frequency ba-nd of said communication current, a signaling device responsive to such signaling frequency band, and means to couple said device with the plate circuit of said second detector tube including a band pass lter proportioned to pass such signaling frequency band.

6. Receiving apparatus comprising a rst and a second electron tube detector, said tubes each provided with a plurality of control grids, a receiving circuit proportioned for response to a given carrier suppressed single side band communication current having a given signaling frequency band, a first and a second source of carrier cturent, said first source of a frequency different from the frequency of the carrier of the communication current and said second source of the same frequency as the communication current carrier, means to connect the receiving circuit with one control grid and said first source to a second control grid of the first detector tube to produce in the plate circuit of said tube the side bands of carrier and the communication current picked up by the receiving circuit, means including an amplifier and tuned circuits to couple the plate circuit of said first detector tube with one control grid of the second detector tube, said means proportioned to select and amplify a particular one of said side bands only, other means to connect said second source with a second control grid and said first source with a third grid of said second detector tube to produce in the plate circuit of said second tube a series of products of demodulation, a signaling device responsive to the signaling frequency band of the communication current, and means including a filter to couple said device with the plate circuit of said Second tube, and said'last mentioned means proportioned to pass only said signaling frequency band.

'7. Receiving apparatus comprising a first and a second electron tube detector, said tubes each provided With a plurality of control grids, a receiving circuit proportioned for response to a given carrier suppressed single side band communication current having a given Signaling frequency band, a first and a second source of carrier current, said first source of a frequency different from the frequency of the carrier of the communication current and said second source of the same frequency as the communication current carrier, means to connect the receiving circuit with one control grid. and said first source to a second control grid of the first detector tube to produce in the plate circuit of said tube the 1 tube With one control grid of the second detector tube, said means proportioned to select and amplify a small portion of the first carrier and a particular one of the side bands only, other means to connect said second source with a second grid of said Second detector tube to produce in the plate circuit of said second detector tube products of demodulation of the first and second carrier and said particular side band, a signaling device responsive to the signaling frequency band of the communication current, and means including a filter to couple said device with the plate circuit of said second tube and said filter proportioned to pass such signaling frequency band only.

8. Receiving apparatus comprising a first and a second electron tube detector, said tubes each provided with a plurality of control grids, a receiving circuit proportioned for response to a given carrier suppressed single side band communication current having a given signaling frefir) quency band, a first and a second source of carrier current, said first source of a frequency higher than the frequency of the carrier of the communication current and said Second source of the same frequency as the communication current carrier, means to connect the receiving circuit with one control grid and said rst source to a second control grid of the first detector tube to produce in the plate circuit of said tube the side bands of the first carrier and the communication current picked up by the receiving circuit, means including an amplifier and tuned circuits to 'couple the plate circuit of said first detector tube with one control grid of the second detector tube, said means proportioned to select and amplify a small portion of the first carrier and a particular one of the side bands only, other means to connect said second source with a second grid of said second detector tube to produce in the plate circuit of said second detector tube products of demodulation of the first and second carrier and said particular side band, circuit means including resistance and capacitance to couple the plate and a selected grid of the Second tube as required to effect superregeneration for which the second carrier acts as the quench frequency, a signaling device responsive to the signaling frequency band of the communication current, and means including a filter to couple said device with the plate circuit of said second tube and said filter proportioned to pass only a band equal to said signaling frequency band.

9. The method of detecting a carrier suppressed single side band signaling current by the superheterodyne reception principle of generating a first local carrier current of a frequency different from the frequency of the carrier of the signaling current and modulating said first local carrier current with the received Signaling energy, selecting a particular side band resulting from such modulation, generating a Second local carrier current of a frequency the same as that of the carrier of the signaling current and mixing the selected side band and the first local frequency carrier With said second local carrier and filtering out the signaling frequency from the products of demodulation.

10. The method of detecting a carrier suppressedn single side band signaling current by the superheterodyne reception principle of generating a first local carrier current of a frequency different from the frequency of the carrier of the signaling current and modulating said first local carrierA current with the received signaling energy, selecting and amplifying a particular side band resulting from such modulation and a small amount of the first local frequency carrier, generating a second local carrier current of a frequency substantially the same as that of the carrier of the signaling current and mixing the amplified energy With said second local carrier and filtering out the signaling frequency from the products of demodulation.

1l. The method of detecting a carrier' suppressed single side band signaling current by the superheterodyne reception principle of generating or firstV local carrier current of a frequency higher than the frequency of the carrier of the rier current of a frequency the same as Athat of thev carrier of the signaling current and mixing the selected side band and said first local carrier with said second local carrier for producing a series of products of demodulation, amplifying selected ones of said products'of demodulation by superregeneration and filtering'out the signaling frequency from the products of demodulation.

12. The method of detecting an upper side band carrier telephone current of generating a first local carrierl current of a frequency different from the frequency of the carrier of the telephoneY current and modulating said first local carrier current with the received telephone current energy, selecting the upper side band resulting from such modulation, generating a second local carrier current of a frequency the same as that of the carrier of the telephone current and mixing said selected upper side band and Some ofthe first local frequency carrier energy With said second local carrier and filtering out the voice frequency band from the products resulting from the demodulation.

LELAND D. WHITELOCK. 

